The International Energy Star Program establishes specifications concerning energy saving. The Energy Star Program sets, for the field of copying machines and MFPs (Multi Function Peripherals), plural operation modes for an image forming apparatus and levels of power consumption required in the respective modes.
One of methods for saving power consumption in the image forming apparatus is to eliminate electric power supplied to a heat roller of a fixing device when the image forming apparatus is in a standby state. However, in the method of saving electric power, when the image forming apparatus starts, it takes time for the temperature of the heat roller to reach fixable temperature.
Therefore, there is a demand for causing the temperature of the heat roller to quickly reach the fixable temperature and reducing power consumption in the image forming apparatus.
Hasegawa (JP-A-2008-122914) discloses an image forming apparatus configured to reduce time required for a rise in the temperature of a heat roller. Hasegawa discloses that electric power is supplied to a heat generating member using an auxiliary power supply device in addition to a main power supply. Hasegawa discloses that the auxiliary power supply device includes a chargeable and dischargeable electricity storage member, a charged electricity detecting unit configured to detect charged electricity of the electricity storage member, and a switching unit configured to switch charging and discharging of the electricity storage member.
A control section transitions a state of the image forming apparatus among plural operation modes. The operation modes include a normal mode and power saving modes. The normal mode is, for example, a copy mode. In the copy mode, a print engine executes printing.
The power saving modes include a ready mode after the end of printing, an electricity saving mode for lowering the temperature of a fixing device, and a sleep mode for inactivating most of components.
Respective mode names of the normal mode and the power saving modes are variously determined according to ranges of levels of electric power specified by the Energy Star Program.
When printing ends, the control section transitions the image forming apparatus from the copy mode to the ready mode. In the ready mode, the control section controls the temperature of the heat roller to be fixed at fixable temperature. When the image forming apparatus does not receive operation from a user for a set time, the control section leaves the ready mode and enters the electricity saving mode.
In the electricity saving mode, the control section turns off main power supply lines except only a part of power saving lines. When the image forming apparatus is not operated by the user for a predetermined time in the electricity saving mode, the control section transitions the image forming apparatus to the sleep mode.
A reduction in power consumption in the electricity saving mode is further explained below.
In the electricity saving mode, the control section lowers the temperature of the fixing device below temperature in a normal standby state of the fixing device.
When the image forming apparatus just finishes printing, the control section gradually lowers the temperature of the fixing device while monitoring the temperature of components of a process system. The process system components indicate a photoconductive drum, a charger, a developing device, a charge removing device, a cleaner, and the like.
In the electricity saving mode, in order to exhaust ozone, the control section needs to supply electric power to a control circuit and a driving section and drive a temperature detecting circuit of the fixing device and fan motors.
Corona discharge by the charger generates ozone. Excessive residual ozone prevents ionization of the air in the next charging. Nitrogen oxides harmful to an image are formed on a photoconductive member by reaction of water due to dew formation and the zone.
Concerning a fan configured to discharge ozone, JP-A-1997-212066 discloses an image forming apparatus in which fans are respectively provided in plural units to make it possible to control cooling by the fans and a flow of the air.
In the electricity saving mode, the control section causes power supply circuits for the heat roller of the fixing device, the fan motors, and the like to continue to operate. A power supply section includes a switching circuit configured to generate low-voltage power. The control section causes the switching circuit to continue to oscillate.
Even in the electricity saving mode, the control section causes the low-voltage power supply to supply electric power to the fan motor of the fan for cooling the process system components and the fan motor of the fan for exhausting ozone generated in high-voltage components. However, the supply of electric power from the low-voltage power supply in the electricity saving mode deteriorates efficiency of use of the power supply.
The operation of the motors and the operation of the temperature detecting circuit in the electricity saving mode increases consumption of electric power on a primary side. Therefore, power consumption of the image forming apparatus as a whole is not improved.